Let's face it. There is a lot of tedium involved in the design of digital products. So much of the design-to-documentation workflow is filled with notating the pesky details of the user experience. Every button, every control matters, and every element must be communicated to the development team and the client in actionable ways.
For me, one of the biggest challenges is going from notebook and whiteboard to shared digital files. I'm always on the look-out for tools that will take some of the agony out of this chore. I'm especially keen to find apps that don't force me to adopt a process model or approach, but do give me enough structure and support to apply my process rigorously. Is this a pipe dream?
Balsamiq calls Mockups a "low fidelity wire-framing tool". I think of this nifty tool as a robust engine for doing real-time, online, collaborative design mock-ups. Mockups has a great library of pre-made interface elements and controls which are all operating system-appropriate (including pretty much all mobile platforms), and what you can't find in the tool's library has likely been developed by someone in the devoted user community. It's easy and intuitive to use, although there are ample online help and tutorials. Mockups saves as an XML file! And, a single-user, multi-platform license is only $79 (although the download is free with very few restrictions).
Check these guys out - you might enjoy a splash of Balsamiq, too!